The invention relates to a brake control and method for controlling brakes in response to a drive defined braking prompt signal.
A device of this type is shown in U.S. Patent Document U.S. Pat. 4,743,072. A brake pressure regulating device for vehicles is described, in which, by way of a brake value generator, the driver defines a braking prompt signal or a desired vehicle deceleration and the actual vehicle deceleration is measured by wheel sensors. The regulating device has a correction value device which, in the event of a deviation between the braking prompt signal and the measure vehicle deceleration, modifies the brake pressure control such that the vehicle deceleration prompted by the driver is reached. This is a classic continuous regulating, in which case several channels are provided for the individual regulating of the deceleration of individual wheels.
U.S. Patent Document No. 4,805,105 describes a pressure control device for road vehicles, in which a regulating intervention takes place only if the difference between the brake pressure prompted by the driver and the actually existing brake pressure is outside a defined range.
European Patent Document EP 0,630,788A1 describes an electronic brake pressure control device for a multi-axle road vehicle, in which load sensors are provided and the brake pressure is regulated as a function of measured axle loads.
U.S. Patent Document U.S. Pat. No. 5,501,512 describes a device for calibrating pressure measuring transducers of an electro-pneumatic brake control of towing vehicles;
When braking vehicles and vehicle trains, the driver, by way of a brake pedal or a brake lever, normally defines a desired value of a brake force or of a desired vehicle deceleration (so-called braking prompt). However, the actual vehicle deceleration on the basis of this braking prompt depends on a plurality of parameters which are not known to the driver, such as the condition of the brake system, the loading of the vehicle, the slope of the road (gradient), the adhesion value between the road and the wheels, etc. For example, in the case of streetcars, it has therefore been attempted to regulate the brake system, the braking prompt was the desired value and the measured actual vehicle deceleration was the actual value of the regulating. However, this resulted in numerous difficulties. A main problem arose because when actuators of rail vehicle brake systems are operated, relatively long dead times occur. In which, in the case of streetcars the dead times are typically in the range of 0.7 seconds. In addition, a relatively long time period (pressure buildup time) is required for building up the braking force which is typically in the range of 1 second.
Because of the inertia of such brake systems and because of diverse natural frequencies of undercarriages and other vehicle components, regulated braking operations can cause considerable jerking within the train formation, which is extremely undesirable. Thus, because of the above-mentioned difficulties, a stable regulating with a feedback in the classic sense, that is, with a continuous signal feedback, is hardly possible.
Another difficulty, which stands in the way of a classic regulating, is that, when the actual value of the vehicle deceleration is defined by differentiating rotational wheel speed signals, which are supplied, for example, by inductive wheel sensors, relatively high percentage-related errors can occur These errors are the result of the scan timing and which, in the case of streetcars, are typically in the range of 100 milliseconds. These errors present an additional difficulty with respect to mastering the regulating.
It is therefore an object of the invention to provide a brake control and a method by means of which a stable braking can be implemented according to the braking prompt defined by the driver in the case of arbitrary parameters influencing the braking.
This object is achieved by the present invention.
The basic principle of the invention consists of arranging a regulating system behind the control, which regulating system will intervene by means of a correction signal only if the deviation between the braking prompt (as a desired deceleration signal) and the actual deceleration of the vehicle is outside a defined range. The corrected brake prompt signal will then be constant for the further control as long as the above-mentioned deviation is within the defined range. A change of the correction signal will not be effective until the above-mentioned deviation is outside the defined range.
The correction signal will be kept constant for one or several clock pulses as long as the difference between the "instantaneous deceleration signal" and the desired deceleration signal is within a defined value range. In contrast, the correction signal is changed from one clock pulse to the next when the instantaneous deceleration is outside this "tolerance band".
In a classic analog control or a conventional digital control, in which, during the entire regulating operation, a control variable is continuously fed back and processed. In the case of the signal processing according to the invention, the instantaneous deceleration, which can be understood to be the control variable, will be processed, that is, used for generating the correction signal, only when the difference between the desired deceleration signal and the instantaneous deceleration, which can be understood to be the "regulating deviation", with respect to its amount becomes too large, that is, is outside the tolerance band. When, in contrast, the regulating deviation is so small that the difference is within the tolerance band, the instantaneous deceleration is not processed and the correction signal is maintained unchanged.
Since the "regulating intervention" takes place only in the case of larger deviations and otherwise the control is unregulated, the initially mentioned dead times and pressure buildup times can be mastered better.
In addition, existing brake systems can be retrofitted with a brake control according to the invention without having to change mechanical components of the existing brake system.
The invention can be implemented as a hardware solution in the form of an electronic circuit as well as a software solution in the form of a computer program for a program-controlled processor or as a combination of the two solutions. Particularly a software-type implementation allows a very cost-effective adaptation of the existing brake control to a certain vehicle and to certain application conditions.
According to the invention, a measured "course" of time-discreet instantaneous deceleration signals calculated from speed signals is smoothed.
According to a further development of the invention, a measured "course" or a "course" of time-discrete instantaneous deceleration signals is smoothed. This takes place in that a smoothed instantaneous deceleration signal is formed from an actual measured value, which represents the instantaneous deceleration of the vehicle , and from measured values of preceding clock pulses. The smoothing takes place by a special filtering where in a number of successively taken measured values are weighted differently and a weighted average value is formed from these weighted measured values. In this case, the weighting is defined such that the measured values which, with respect to time, are close to the actual measuring point in time are weighted higher than the measured values which are more remote with respect to the time. In contrast to a frequency filtering, for example, by means of a low-pass filter, no signal transformations are therefore obtained in the time range. By such a smoothing of the course of the deceleration signal, errors can be reduced which are made during the measuring or during the calculation of the individual time-discrete instantaneous decelerations. On the whole, this results in a smoother course of the correction signal and therefore in braking operations with fewer jolts.
According to a further development of the invention, a "correction signal gradient" formed by two successive correction signals, in the event of the exceeding of or the falling below a defined positive or negative maximal gradient, is limited to this maximal gradient. This has the advantage that deceleration jolts and resulting force impulses at the vehicle or within a vehicle formation during the braking operation are further minimized. This reduces the mechanical stress.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.